1. Field of the Invention
The present invention refers to a machining tool assembly for cuttingly machining of an at least partially closed inner surface of a workpiece, e.g. the inner surface of a blind bore provided in a workpiece.
In practice, often the need arises to cuttingly machine a workpiece in its interior along one of the inner surfaces thereof. For instance, the workpiece might have a cylindrical bore, the diameter thereof having to be enlarged along a certain portion. Usually such machining operation is performed on a turning lathe by means of a tool assembly which comprises an essentially cylindrical tool support, the end thereof being equipped with a machining tool, e.g. a cemented carbide cutting steel or the like. The tool support including the machining tool is inserted into the opening to be further machined, whereby a relative rotational movement between the machining tool and the workpiece to be machined is effected during the cutting operation. This may be performed either by rotating the machining tool and fixing the workpiece or by rotating the workpiece to be machined and fixing the machining tool.
In order to enable such machining of the interior of a workpiece to be effected, the tool assembly has to be inserted into the cavity, e.g. the blind bore of the workpiece, the inner surface of which has to be machined. It is thereby necessary that the total outer diameter in radial direction of the tool support and the machining tool be less than the diameter of the opening provided in the workpiece. In this connection a number of partially contrary requirements have to be met:
In the interest of the highest possible stability, and thereby of the best possible machining accuracy, the shaft portion of the tool assembly which supports the machining tool has to be rigid and insensitive to bending; consequently it should have a large diameter. As the machining tool itself has to protrude from the shaft surface, the consequence is that the useful width of the tool is comparatively small and the tool assembly may be used but within a very narrow machining range.
To the contrary, it is desirable to design the shaft supporting the machining tool with a comparatively small diameter in order to increase the useable machining range of the tool assembly. Such a proceeding, however, will result in a decreased rigidity of the assembly and therefore in a decreased machining accuracy, since the shaft of the tool assembly is clamped but at one side and is thereby subjected to a pronounced bending stress.
2. Prior Art
Machining tool assemblies known up to know suffer from the disadvantage that they are subjected to more or less pronounced flexural vibrations during the machining operation of the workpiece, with the result that, in the best case, a decreased accuracy of the machining operation must be accepted, but, in the worst case, an early destruction of the quite expensive machining tool occurs. Sometimes a cutting of workpieces is not reliable or even impossible with such a tool assembly due to the occurence of the aforementioned flexural vibrations, so that the machining of the workpiece has to be done by means of other processes, often with the need to use very expensive special tools.
A machining tool assembly which appears similar on the first sight to the machining tool assembly provided by the present invention is disclosed in the French Pat. No. 1,233,868. This assembly is intended to machine the internal surfaces of a workpiece as well and comprises also a rod-like tool support, the end thereof receiving a radially adjustable machining tool. However a very important difference may be seen in the fact that the machining tool assembly according to the aforementioned French Patent refers not to a tool for rotative machining, but to an oscillating tool which is used to cut longitudinal grooves, parallel to the axis, into the internal surface of a bore. The assembly according to the French Patent could not be used for the purpose of the present invention, i.e. to partially increase the diameter of a bore in a workpiece or to provide annular, coaxial grooves in the inner surface thereof.